Ethylene and propylene are very important basic raw materials in petrochemical industry, which are produced by cracking hydrocarbon comprising of paraffin compounds such as natural gas, naphtha, gas oil, etc, at a high temperature at least 800° C. in the presence of steam. To increase the yield of ethylene and propylene from hydrocarbon steam cracking, conversion rate of hydrocarbon or olefin selectivity has to be increased. However, the pure hydrocarbon steam cracking itself has limit in increasing hydrocarbon conversion rate or olefin selectivity. So, various methods have been proposed to increase the yield of olefin.
One of those methods proposed to increase the yield of ethylene and propylene so far is steam cracking using a catalyst. U.S. Pat. No. 3,644,557 describes a method using a catalyst comprising magnesium oxide and zirconium oxide, U.S. Pat. No. 3,969,542 describes a method using a catalyst containing calcium aluminate as a basic component, U.S. Pat. No. 4,111,793 describes a method using manganese oxide catalyst supported by a zirconium oxide, European Patent Publication No. 0212320 describes a method using an iron catalyst supported by a magnesium oxide, and U.S. Pat. No. 5,600,051 describes a method using a catalyst comprising of barium oxide, alumina and silica. In addition, PCT No. 2004/105935 describes a method using a catalyst comprising of potassium magnesium phosphate, silica and alumina. These catalysts were known to increase the yield of olefin by acting as a heating medium during hydrocarbon steam cracking, but the increase of olefin yield was not significant, compared with when an inactive carrier was used.
Russian Patent No. 1,011,236 describes a potassium vanadate catalyst modified by boron oxide and alumina carrier. However, using such an alkatimetal oxide or potassium vanadate as a catalyst did not increase olefin yield much and even dragged down the yield unavoidably at high temperature for the hydrocarbon decomposition. More precisely, the above catalysts might exist in the liquid phase inside of the high temperature cracking reactor owing to the low melting points of the catalyst components, and these catalyst components are volatilized by fast circulation of reaction gas, so that the catalyst activity is decreased with respect to the reaction time.
U.S. Pat. No. 7,026,263 describes a method using a hybrid catalyst comprising of molybdenum oxide, alumina, silica, silicalite and zirconium oxide. With this catalyst, reaction carried on at low temperature with low hydrocarbon flow. But, the reaction temperature needs to be raised to at least 800° C. as hydrocarbon flow increases. The above catalyst, however, has very low thermal stability at high temperature so that it is melted or lost its catalytic activity.
Therefore considering economic aspects of hydrocarbon steam cracking or to avoid the complexity of processes, a novel catalyst that is able to enhance olefin yield significantly compared with an inactive carrier catalyst and has enhanced thermal stability at high temperature is required.